Radiant heating pipe

ABSTRACT

Provision is made of a radiant heating pipe  10  which is designed to conduct hot gas through a central portion  14  in a preferred direction of flow SV, directed away from the burner  22 , into at least one return portion  16, 18  and preferably at least partially back into the central portion  14 , such that a recirculation flow through the radiant heating pipe  10  is produced overall. The smallest flow cross section D A  for the gas in a zone  24 , close to the burner, of the central portion  14  is smaller than the smallest flow cross section D E  in a zone  26  remote from the burner. Preferably, the radiant heating pipe  10  according to the invention has a waist at the transition from a branching portion 13, close to the burner, to the central portion  14.

The subject matter of the invention is a radiant heating pipe displaying improved flue gas recirculation.

Radiant heating pipes are used for the indirect heating of industrial furnaces with fuel. Combustion occurs inside the radiant heating pipe and the resultant thermal energy is transferred to the material to be heated by radiant heat. Such radiant heating pipes are described, for example, in publication DE 20 2008 009 065. Here, special radiant heating pipes are formed in the so-called double-P structure configuration.

In general, a radiant heating pipe has a burner connection in which the burner is located. Adjoining the burner connection is a branching portion and, adjoining that, a central portion. The fuel gas supplied to the burner and the supplied air oxidize in the radiant heating pipe. The oxidation zone takes up a larger space in the radiant heating pipe. The gas participating in the combustion moves through the central portion into at least one return. portion that is connected to the central portion via an intermediate portion, comprising at least one pipe bend piece. The central portion and the return portion form a loop that, ultimately, returns the flue gas to the branching portion. There, part of the flue gas can be exhausted through the flue gas outlet. In doing so, it may heat the supplied air, for example, and, furthermore, it may be returned to the central portion, so that at least a part of the flue gas is recirculated. Radiant heating pipes exhibiting the double P structure configuration comprise two return portions that—like the central section—also have generally the form of a cylinder. In doing so, the diameter of the central portion is typically greater than the diameter of respectively one of the two return portions.

FIG. 2 illustrates a prior-art radiant heating pipe 10. The radiant heating pipe 10 comprises a central portion 14 that has the form of a cylinder. The central portion 14 thus has a diameter that is constant along the length of the central portion 14. In such a radiant heating pipe, irregular temperature distributions in the radiant pipe wall, for example the central portion, as well as undesirable CO values and NOx values can be observed.

The described radiant heating pipes having the double-P structure configuration of prior art have been successfully used. However, in each of these radiant heating pipes, temperature peaks of the temperature ditribution were found, for example, in the initial section of the central portion. This may be undesirable. In addition, the search for possibilities of reducing CO and NOx emissions resulting from the combustion process in the radiant heating pipes has been ongoing.

It is the object of the invention to provide an improved radiant heating pipe that minimizes the described disadvantages of prior art and exhibits reduced CO and NOx emissions.

In accordance with the invention, this object is achieved with a radiant heating pipe displaying the features of Claim 1.

The inventive radiant heating pipe comprises a burner connection. This is a hollow, in which a burner can be installed. The burner connection has a burner connection opening. Adjoining the burner connection is a branching portion. A burner may extend through the burner connection opening into the branching portion or terminate in the burner connection. A central portion with a zone of the central portion close to the burner adjoins said central portion. Furthermore, the central portion comprises a zone remote from the burner, said central portion being downstream of said zone close to the burner. Between the zone close to the burner and the zone remote from the burner, there may also be provided additional zones of the central portion. The zone close to the burner and the zone remote from the burner may, respectively, extend over a more or less long distance along the central portion or have a length of zero. At least one return portion is located next to the central portion. The at least one return portion is connected to the central portion via an intermediate portion as well as via the branching portion. The central portion and the return portion, together with intermediate portion and the branching portion, form a loop in which a circulating flow may form.

The zone close to the burner and the zone remote from the burner of the central portion may each have different diameters along the central portion (along axial direction) so that, respectively, a smallest diameter is defined at least in one location of the zones. The smallest diameter of the zone close to the burner is smaller than the smallest diameter of the zone remote from the burner. Circulating flue gas moves through the central portion into the at least one return portion and back to the branching portion. Part of the flue gas leaves the radiant heating pipe through a flue gas outlet, e.g., near the burner, and may thus heat the supplied air, for example. Part of the gas may move back into the central portion and recirculate via a return portion. With the use of such a radiant heating pipe in accordance with the invention it is possible, in contrast with prior art, to achieve reduced CO and NOx values and a. more uniform wall temperature distribution.

Preferably, the cross-section of the radiant heating pipe, in any event the central portion, is circular. However, the central portion and the at least one return portion may also have different cross-sectional forms. In the case of a non-circular cross-section of the central portion, both the zone close to the burner and the zone remote from the burner have a cross-section displaying the smallest area, wherein the smallest cross-sectional area of the zone close to the burner is smaller than the cross-sectional area of the zone remote from the burner.

In the central portion, the flue gases flow in a preferred direction from the zone close to the burner into the zone remote from the burner of the central portion. Preferably, the diameter or cross-section of the central portion of the pipe body widens in the direction of the preferred direction of flow. Preferably, the diameter or cross-section of the central portion of the pipe body widens in the direction of the preferred direction of flow, without narrowing again (monotone). The central portion may act as the diffusor and convert the dynamic pressure to static pressure.

Preferably, the pipe body of the central portion is configured so as to widen conically in the preferred direction of flow.

Preferably, the ratio of the smallest diameter of the zone close to the burner to the smallest diameter of the zone remote from the burner is less than two thirds. In the case of non-circular cross-sectional areas, the smallest cross-sectional area of the zone close to the burner amounts to preferably at most two thirds of the area of the smallest cross-section of the zone remote from the burner.

A burner may be installed in the burner connection and thus be connected to the radiant heating pipe. Usually, a burner has a basically cylindrical shape. Preferably, the burner connection is adapted to the basic shape of the burner. The diameter or cross-section of the burner connection, in particular the opening, is preferably greater than the smallest diameter or cross-section of the zone close to the burner.

Preferably, the radiant heating pipe comprises a total of two return portions, each forming a loop with the central portion. In this manner, it is possible to create a relative large surface of the radiant heating pipe. Preferably, the central portion has a longitudinal axis, and a return portion extends parallel to the longitudinal axis on one side of the can portion. The other return portion extends in parallel direction on the opposite side of the central portion.

Existing return portions and the central portion are preferably located on one plane in order to achieve an overall compact design.

Preferably, the radiant heating pipe comprising two return portion has a so-called double-P structure configuration.

The central portion and the return portion as well as additional portions of the radiant heating pipe may be made of sheet steel, cast steel or other materials. The radiant heating pipe may also be made of ceramic material.

A burner such as, for example, a recuperator, e.g., a split recuperation burner, or a regenerator burner, may be connected to the radiant heating pipe. Particularly preferably, the burner is adapted for flameless oxidation.

Advantageous embodiments of the invention can be inferred from the dependent patent claims and the description. Advantageous developments are obtained by combining at least one of the independent claims displaying the features of one or more dependent claims. FIG. 1 of the drawings is designed to augment the description. FIG. 2 is not the subject matter of the present application. The drawings are schematic representations. They show in

FIG. 1 a radiant heating pipe in a double-P structure configuration;

FIG. 2 a prior-art radiant heating pipe, said embodiment not being the subject matter of the present application.

FIG. 1 shows a sectional view of art inventive radiant heating pipe 10 comprising a burner connection 12, a branching portion 13, a central portion 14, a first return portion 16 and a second return portion 18. The central portion 14 adjoins the branching portion 13. In the preferred direction of flow S_(V) toward the central portion 14, there is provided an intermediate portion 20 that has two arcuate pipe sections and is connected to the central portion 14. The first return portion 16 and the second return portion 18 are connected—via the arcuate pipe sections of the intermediate portion 20—to the central portion 14 on the side of the radiant heating pipe 10 that faces away from the burner connection 12. The first return portion 16 and the second return portion 18 are connected to the branching portion 13, so that a total of two loops with one return portion 16, 18, respectively, do exist. There may also be only one loop, i.e., a return portion 16, 18 or, if more than two return portions 16, 18 are provided, there may be appropriately more loops.

A burner 22 is installed in the burner connection 12. In doing so, this may be a split recuperation burner, for example. The central portion 14 has a zone 24 close to the burner and a zone 26 remote from the burner. The zone 24 close to the burner of the central portion 14 adjoins the branching portion 13. The zone close to the burner has the smallest diameter D_(A). The central portion 14 is connected to the intermediate portion 20 via the zone 26 remote from the burner. The zone 26 remote from the burner—and this is applicable also to the zone 24 close to the burner—may extend along a length along the central portion 14, or it may have a length of zero. The zone remote from the burner has the smallest diameter D_(E). The smallest diameter D_(E) of the zone remote from the burner is greater than the smallest diameter D_(A) of the zone close to the burner.

The radiant heating pipe as in FIG. 1 has a waist at the transition between the branching portion 13 and the central portion 14. Preferably, the ratio of the smallest. diameter D_(A) of the zone close to the burner to the smallest diameter D_(E) of the zone remote from the burner is less than two thirds. The opening 21 of the burner connection 12 is preferably greater than the smallest diameter D_(A) of the zone 24 close to the burner. A preferred direction of flow S_(V) is prespecified in the central portion 14, said direction of flow pointing from the branching portion 13 to the intermediate portion 20.

The diameter of the central portion 14 widens in the direction of the preferred direction of flow S_(V) and is conical. For example, it is also possible for the central portion 14 to initially taper downstream of the branching portion 13 in a zone 24 close to the burner in order to subsequently widen again in a conical manner. In the exemplary embodiment, the first return portion 16 and the second return portion 18 are straight pipe pieces with a constant circular diameter exhibiting the same cross-sectional area. Each of them extends parallel to the longitudinal axis L of the central portion 14. The central portion 14, the first return portion 16 and the second return portion 18 are located on one plane and a form a double-P structure configuration of the radiant heating pipe. Alternatively, for example, only a single return portion 16, 18 may exist and the radiant heating pipe 10 may thus form a P-configuration of the radiant heating pipe.

The radiant heating pipe 10 overall is made of heat-resistant sheet metal, tubular metal or cast steel; however, it may also be made of ceramic. The burner 22 has at least one connection for gas 28 and one connection for air 30. Furthermore, the burner 22 has one or more gas outlets 34.

The radiant heating pipe 10 described so far operates as follows:

Gas and air are fed to the burner 22 via appropriate connections. On the burner, the gas exits through at least one gas outlet 32, and the air exits via air outlets 24 at high speed. The gas and the oxygen of the air react in the radiant heating pipe 10. The hot gas flows through the central portion 14 in the preferred direction of flow. Due to the widening of the cross-section of the central portion 14, a reduction of the flow rate of the gas and an increase of the static pressure occur. The gas flow is split in the intermediate portion 20. One part of the gas flows through the first return portion 16, the other part flows through the return portion 18. The gas flow enters the volume of the branching portion 13. There, the gas flow is partially discharged through a flue gas outlet and can be used, for example, for heating the supplied air. The gas flow is partially mixed with fresh gas and air. In this manner, an advantageous operation with flame less oxidation can be achieved. The gas flowing through the radiant heating pipe 10 heats the radiant heating pipe 10, said pipe releasing radiant thermal energy into the industrial furnace, for example. The exemplary embodiment in accordance with the invention exhibits an evened out temperature distribution on the radiant heating pipe wall.

Provision is made of a radiant heating pipe 10 which is designed to conduct hot gas through a central portion 14 in a preferred direction of flow S_(V), directed away from the burner 22, into at least one return portion 16, 18 and preferably at least partially back into the central portion 14, such that a recirculation flow through the radiant heating pipe 10 is produced overall. The smallest flow cross-section D_(A) for the gas in a zone 24, close to the burner, of the central portion 14 is smaller than the smallest flow cross-section D_(E) in a zone 26 remote from the burner. Preferably, the radiant heating pipe 10 according to the invention has a waist at the transition from a branching portion 13, close to the burner, to the central portion 14.

LIST OF REFERENCE SIGNS

-   10 Radiant heating pipe -   12 Burner connection -   13 Branching portion -   14 Central portion -   16 First return portion -   18 Second return portion -   20 Intermediate portion -   21 Opening -   22 Burner -   24 Zone close to the burner -   26 Zone remote from the burner -   28 Connection for gas -   30 Connection for air -   32 Gas outlet -   34 Air outlet -   D_(A) Smallest flow cross-section of the zone close to the burner -   D_(E) Smallest flow cross-section of the zone remote from the burner -   S_(V) Preferred direction of flow 

1. Radiant heating pipe (10) comprising: a burner connection (12), a branching portion (13), a central portion (14) and at least one return portion (16, 18) located next to the central portion (14), said return portion (16, 18) forming a loop with the central portion (14), wherein the central portion (14) comprises a zone (24) close to a burner, said zone adjoining the branching portion, and a zone (25) remote from the burner connection (12), and wherein the zone (24) close to the burner has a smallest diameter (D_(A)) that is smaller than a smallest diameter (D_(E)) of the zone (26) remote from the burner.
 2. Radiant heating pipe as in claim 1, wherein a cross-section of the central portion (14) widens in a preferred direction of flow (S_(V)).
 3. Radiant heating pipe as in claim 2, wherein the central portion (14) is conical.
 4. Radiant heating pipe as in claim 1, wherein a ratio of the smallest diameter (D_(A)) of the zone close to the burner to the smallest diameter (D_(E)) of the zone remote from the burner is less than ⅔.
 5. Radiant heating pipe as in claim 1, characterized in that a diameter of an opening (21) of the burner connection (12) is greater than the smallest diameter (D_(A)) of the zone (24) close to the burner.
 6. Radiant heating pipe as in claim 1 further comprising a total of two return portions (16, 18), each forming a loop with the central portion (14).
 7. Radiant heating pipe as in claim 6, wherein the central portion (14) has a longitudinal axis (L), and that the return portions (16, 18) extend parallel to the longitudinal axis (L) of the central portion (14).
 8. Radiant heating pipe as in claim 1, wherein the central portion (14) and the at least one return portion (16, 18) are located on one plane.
 9. Radiant heating pipe, wherein the central portion (14) and the at least one return portion (16, 18) consist of sheet steel or cast steel.
 10. Radiant heating pipe as in claim 1, wherein the burner (22) is connected to the burner connection (12).
 11. Radiant heating pipe as in claim 10, wherein the burner (22) is a burner (22) adapted for flameless oxidation. 